In hearing aids of this kind, there are a number of challenges in making a reliable and easy to operate electro-mechanical construction. The in the ear piece is difficult for the user to place correctly in the ear, and the electric and mechanical connection of the lead with the behind the ear casing part also constitutes a vulnerable element as leads must be exchangeable in order that the user may have a lead with length and shape according to the individual physiognomy and head shape. Further, it may be difficult for some users to determine whether the apparatus in hand is to fit the right side or the left side ear.